1. Field of the Invention
The present invention relates to a photo-curable composition that includes a polymerizable compound, a polymerization initiator and a dye and that is curable with radiation.
2. Description of the Related Art
Aqueous ink compositions have low water resistance and may easily cause smearing, when printed on standard paper. Further, when printed on non-water absorbing recording materials such as plastics, aqueous ink compositions have also been known to promote deficiencies such as failure of image formation due to poor adhesion of ink droplets, the need for allowing the ink to dry, which prevents stacking of recording materials immediately after printing because of the extremely slow evaporation of the solvent of the ink, and smearing of images.
An ultraviolet-curable ink including a polyfunctional monomer having good adhesion to non-water absorbing recording materials has been proposed as a suitable ink composition for printing on non-water absorbing recording materials (see for example Japanese Patent Application National Publication (Laid-Open) No. 2001-512777). Since this ink is of a water dispersion type, however, it dries slowly and is insufficient for forming full-color images. To improve drying properties, volatile organic solvents have been used for the inks. For rapid drying, however, it is necessary to use a highly volatile solvent such as methyl ethyl ketone or ethanol as a main component.
In view of these problems, an inkjet recording ink has been proposed which is capable of being cured and fixed by radiation rather than by volatilization of ink solvents (see for example Japanese Patent Application Laid-Open (JP-A) No. 05-214279). Since this ink includes a pigment dispersion as a coloring component, it may cause nozzle clogging due to the agglomeration of the pigment, so that it may be difficult to maintain stable ink ejection.
When pigments are used as coloring materials, transparency may be reduced, or color tone may be insufficient, so that it may be difficult to obtain photographic image quality. In order to solve this problem, there is proposed an ultraviolet-curable ink using a dye as a coloring material (see U.S. Pat. No. 4,303,924). However, this ink may easily cause an undesirable polymerization reaction during storage, and therefore has the problem of insufficient storage stability. Further, when conventional dye compounds are used as alternatives to pigments, they have insufficient light fastness, and therefore the color of the dye may fade during or after curing. Moreover, since the ink also contains electrically-conductive salts, the solubility of the salts in the ink may sometimes be low so that printing defects may be caused by the precipitation of the salts after long-term storage.